Electric control circuit



Feb. 26, 1946. B 5.l |||GG|NS 2,395,626

` ELECTRIC CONTROL CIRCUIT Filed Oct. 7, 1943 2 SheetS-Sheet 1 Fig. l. ,5 l

[ A i ,TINE/7 60A/IML Bertram G.H grw,

Feb. 26, 1946. B, G. i-nGGlNs 2,395,626

ELECTRIC CONTROL C IRCUIT Filed oct. 7, 1943 2 sheetssheet 2 Inventor: Bertram G. Higgins,

His Att-omweg.

Patented feb. 26, 1946 ,ouaoso PATENT orrlc ELECTRIC CONTROL CIRCUIT Bertram G. Higgins, Rugby, England, assigner to General Electric Company, a corporation of New York pp'licationbctober 7, 1943, Serial No. 505,316 In Great Britain October 6, 1942 s cmmacl. 11i-119) l l My invention relates to improved electric control circuits and particularly to improved control or regulating circuits for regulating an electrical condition of an alternating-current load circuit which is intermittently energized through controlled electric valve means.

Inresistance welding, for example, it is essen,- tial to high quality welds that the current supplied to the work be maintained substantially independent of line voltage fluctuationsl and changes in circuit constants, due forinstance, to changes in the position o! the work pieces in the throat of the welding machine. Utilizing the actual load current as a controlling influence provides satisfactory regulation rafter the rst cycle or ilrst few cycles of each period of energization'andin some cases,.may provide an ac ceptable control, However, in many cases, it is essential that the current 'be regulated during the nrst cycle or, cycles of each/period of V'energization and this becomes particularly important as the periods of energization are shortened in length. In accordance with'the teachings of the present invention, Iprovide a new and improved Aelectric control circuit for regulating an electrical condition such as the current supplied to an intermittently energized load circuit.

It is an object of my invention to provide a new and improved electric control circuit.

It is another object o! my invention to provide a new and improved circuit for regulating an electrical condition oi a load circuit which is energized intermittently by alternating current through controlled electric valve means.

It is still another object of my invention to provide an improved control circuit particularly adapted for resistance welding applications in which a predetermined value of `welding current is supplied to the load circuit during each cycle of energization of the load circuit.` f

4In accordance .withthe illustrated embodiment of my invention, the welding transformer is energized from anA alternating current supply circuit :wave that each of the reversely connected electric valvesV is rendered conductive. In accordance with the present invention. the regulating circuit produces a sinusoidal voltage which has a phase displacement during periods of deenergization of the load circuit dependent upon the magnitude 5 of a preset control voltage. During periods of energizationof vthe load circuit, the sinusoidal voltage has d variable phase displacement dependent upon the resultant of this preset voltage, a reference voltagel obtained from'the timer control, and a voltage responsive to the current supplied to the load circuit. Inasmuch as `the reference voltage obtained from the timing circuit and the voltage responsive to the load cur`\\ rent both disappear during periods ofdeenergiza- \f l5 tion, these voltages may be introduced into the control circuit in seriesand the transfer from "off-time to on-time" regulation accomplished without any complicated switching arrangement.

My invention will be better understood by rei'- erence to the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims. In the drawings, Fig. 1 illustrates diagrammatbvcally one embodiment of -my invention and Fig. 2 is a schematic representation of the modincation of Fig. 1 showing the component. parts of the lcontrol in more detail.

Referring to Fig. 1 of the drawings, I have shown my invention incorporated in a system for controlling the energization .of a welding transformer I0 having a primary winding I I connected with a single phase alternating-current supply circuit I2 through a. pair of reversely connected electric valve means I3 and I4. 'Riese electric valve means are .identical and, as illustrated, may be of the type comprising an anode I5, a. cathode of conducting liquid I6, such as mercury, and an immersion-ignitor control member I1. The energization of the control members II of the electric valve means I3 and il is controlled by the excitation circuits illustrated dla-v grammatically at BI- and B2, respectively. These circuits transmit impulses of current to the control `member I1 for a number of cycles of the supply circuit I2 determined by a timler control illustrated diagrammatically at A and at instants in the positive half cycles of `anode voltage of the valve means I3 and I4 determined by a regulating circuit'illustrated diagrammatically at C. I'he timer control is preferably of the type that produces a vsinusoidal voltage of intermittent character corresponding to the vdesired energize.- tion of the load. The timer may be to advantage v of the type'described in British Patent 418,374 or 55 British Patent 528,247. The excitation circuits BI and B2 are energized in accordance with the output of the timer control A andthe regulating circuit C by means of a control and amplifying circuit illustrated diagrammatically at D. A supply of alternating current control voltage for the various circuits is provided by the alternatingcurrent circuit I3 which may be energized from the supply circuit I2 through a transformer I3. The circuit I8 provides 'a source of unregulated alternating voltage for the timer control A, the excitation circuits BI, B2, and the control and amplifier circuit D. A source of regulated voltage for the regulating circuit C is obtained from the circuit I3 by means of a regulating transformer illustrated schematically at E,

A detailed understanding of the illustrated embodiment of my invention may be had by reference to Fig. 2 which illustrates in detail the circuits illustrated diagrammatically at BI, C and D in Fig. l. Referring now to Fig. 2, control impulses of current are transmitted to the control member I1 of the electric valve means I3 by a control or firing valve 23, preferably of the gas-filled type and having the anode-cathode circuit thereof connected between the anode I and control member I1 of the electric valve means I3 through contacts of switches 2| and 22 and a current-limiting resistor 23. The electric valve 23 is provided with a control member or grid 24 which is energized to determine the number of cycles and the instant in each cycle that electric valve I3 is rendered conductive. The circuit of the control member 24 includes a resistor 25 for impressing a negative or hold-ofi" bias on the control member 24 and the secondary winding 23 of a transformer 21 for impressing on the control member a periodic voltage of peaked wave form for an interval determined by the timer control A and having a phase relation determined by the regulating circuit C. The circuit of the control member 24 also includes a current-limiting resistance 23 and a transient-suppressing capacitor 29 connected between the control member and the cathode thereof. The hold-off or negative bias voltage across the terminals of the resistor is derived from the alternating-current circuit I8 through a transformer 33 and a full-wave rectifier 3|. The excitation circuit for the control member I1 of electric valve I4 is essentially the same as that described in connection with the electric valve means I3 and has been illustrated diagrammatically at B2. The firing or turn-on voltage for the excitation circuit for valve means I4 is supplied by the secondary wind- 'ing 32 of the transformer 21 and has the proper instantaneous polarity to control the electric valve i4.

The primary winding 33 of the transformer 21 is energized in accordance with the output of the regulating circuit C and, for periods determined by the timer control circuit A, by the conjoint action of electric valves 34 and 35 of the control and amplifier circuit D. These electric valves are preferably of the high-vacuum tetrode type. The anode-cathode circuits of electric valves 34 and 35 are connected in series and across the direct-current lines 33 and 31 of a directcurrent control voltage supply derived from the alternating-current circuit I3 by means of a rectifier and iilter circuit illustrated generally by the numeral 33. A resistor 39 is connected between the cathode of valve 34 and the anode of valve and a resistor 43 is connected between the cathode of valve 35 and the negative of direct-current line 31. As illustrated the resistor assenso 33 is the load resistor and provides the voltage from which the primary winding 33 of the transformer 21 is energized. The resistor 43, in the cathode connection of valve 35. provides a source of negative bias for this valve. The screen grid of valve 34 is connected with the positive line 33 of the direct-current circuit through a resistor 4I and the screen grid of valve 35 is connected to a. suitable voltage intermediate the conductors 33 and 31 established by the terminal 42 of a voltage-dividing resistor 4'3. 'Ihe electric valve 34 may be considered a keying valve and its function is to maintain the resistor 33 deenergined during periods when it is desired that the welding transformer I3 be deenergised. To this end, the control member of valve 34 is energized with a negative bias voltage impressed across resistor 44 by a rectiner bridge 45 and a transformer 43 having the primary thereof energized from the alternating-current circuit I3. A positive or turn-on" voltage is derived from the output of the timer control A by means of transformer 41 and a rectifier bridge 43 and impressed on a resistor 43 which is connected in series with the negative bias resistor 44 and a current-limiting resistor 53 in the cathode-to-control-member circuit of electric valve 34. The bias voltes of resistors 44 and 43 are so proportioned that the voltage of resistor 44 biases the valve 34 to cutoff during periods of no voltage output. of the timer. In order that the phase of the voltage appearing across resistor 33 corresponds to the output of the regulating circuit C, the control member of the valve 35 is energized from the sec- Ondrv Windins 5I of an output transformer 52 of a phase-shifting circuit 53. 'Ihe circuit of the control member of the valve 35 also includes a current-limiting resistor 54 and the bias resistor 43. Thus, the circuit D operates to impress a periodic voltage of substantially sinusoidal wave form on the primary winding of the transformer 32 during the periods that electric valve 34 is rendered conductive by the timer control and with a phase relation dependent upon the voltage of the output transformer 52 of the regulating circuit C.

The manner in which the output voltage of circuit C is derived from the timer control and load circuit will now be described. 'I'he phaseshifting circuit 53 is of the bridge type and comprises a midtapped secondary winding 55 of a transformer 53 having the primary winding 51 energized from the alternating-current circuit I3. The halves of the midtapped winding 55 provide two arms of the bridge circuit, the other two of which include a capacitor 53 and the alternating-current terminals of va rectifier bridge 53. The primary winding of the output transformer 52 is connected between the midtap of the secondary winding 55 and the common terminal of the rectifier bridge 33 and the capacitor 53. As will readily be understood by those skilled in the art, the effective alternatingcurrent resistance of the bridge circuit 53 may be controlled by controlling the impedance connected across the direct-current terminals thereof. As a means for providing such a controllable impedance, I employ an electric valve, preferably of the high-vacuum tetrode type. having the snode-cathode circuit connected acro the direct-current terminals of the rectifier bridge 53 through a resistor 3| and an indieatingsmmeter 32. 'I'he valve 33 is provided with a screen grid which is maintained at a positive potential with respect to the anode by vmeans of a resistor I 2,898,026 v88 connected between the screen grid and the terminal ofresistor 8| remote from the anode.

The valve 88 is also provided with a control meml ber or grid 84 which is energized in accordance with the resultant of three voltages impressed respectively on a resistor 88, a resistor 88, and a resistor 81. The cathode-to-control-member circuit includes a portion of the resistance 81 determined by the position of an adjustable tap 88, a portion of the voltage of resistor 88 determined by the position of an adjustable tap 88, and the total voltage of resistor 88. A resistprise an electric discharge device 18 of the double-diode type and a transformer 14 having a midtapped secondary winding 18. The primary winding 18 of the transformer 14 is energized in accordance with vthe welding or load current by means of -a current transformer 11 associated with one of the line conductors of the altemating-current circuit |2. The circuit of the primary winding 18 is completed from the terminals of the current transformer 11 through an indicating ammeter 18, a manual switch 18, and a normally closed contact 88 of an electromagnetic relay 8I. The ratio of current in the load circuit to the voltage across the terminals of the current transformer may be adjusted by taps on the resistors11a which shunt the current transformer. The relay 8| has the operating coil 82 thereof energized in accordance with the direct-current output voltage of a rectifier bridge 88 having the alternating-current terminals thereof energized in accordance with the voltage appearing across the terminals oi' the current transformer 11. The relay 8| is also provided with a normally open contact 84 which completes an energizing circuit for an indicating lamp 88 when the output voltage of the rectifier bridge exceeds a predetermined value. A

normally closed contact 88 of the relay 8| controls the energizing circuit of resistor 88. A recl 84 of a biphase'rectirler circuit including a mid- -tapped secondary winding 88 of the transformer 88 and apair of electric valves 88 and 81 which may, for example, be of the three-element gaseous discharge type. 'I'he valves 88 and 81 are provided with control members -88 which are energized to render the' electric valves 88 and 81 conductive intermittently in accordance with the output of the timer control circuit A. `The transformer |88 and a rectier bridge |8|.

control members are normally maintained nega tive by the voltage appearing across a bias resistor 88 which may, to advantage, be energized from the altemating-current 8 through a A "turn-on" or positive voltage is impressed on the control members 88 by a resistor '|82 which is energized from the output circuit of the timer control A through transformer |88 and the rectiiler bridge |84. The circuit of each of the control members 88 includes a current-limiting resistor |88 and a transient-suppression capacitor |88 which is connected directly between the --cathodes and the respective control members 88 of the electric valves 88 and 81. Thus the voltage across the resistance 88 is intermittent corresponding to the output voltage of the timer control A and is regulated in magnitude by the operation of the regulating transformer E. A manual switch |81 may be included in the energizing circuit of the timer control to control the initiation of energization ofthe load.

AThe circuit of the control member 84 of the electric valve 88, therefore, contains a source of negative bias of preset value appearing across resistor 81 and determined by the position of the slider 88, a second component of voltage having a positive polarity which occurs intermittently at intervals determined by the timer voltage and a third component which is of negative polarity and variable in accordance with the current supplied to the load.

A better understanding of the objects and advantages of my invention may be had by a consideration of the operation of the system illustrated in Fig. 2 `and described in detail in the preceding paragraphs. Let it be assumed that the alternating-current supply circuit l2 has been energized by the closing of suitable switching means (not shown), and that the switches 2|, 22, 18 and 82 have been closed and switch |81 is open. It is also assumed that the cathodes of .all of the electric valves are at proper operating temperature. Uunder these conditions, no welding current is flowing and no voltage is produced across the resistor 88 by current transformer 11 and rectiiier 18. The valves 88 and 81 are maintained nnconductive by the bias of resistor 88 so that no voltage appears across the resistor 88.

The energization of the control member 84 of the electric valve 88 associated with the phaseshifting circuit 88 is under these conditions determined by the magnitude oi' the preset voltage appearing across a portion of a resistor 81 as determined by the position of the slider 88 which, therefore, provides a manual heat-control adjustment. 'I'he keying Avalve 84 is maintained non- .conductive by the negative bias appearing across v the resistor 44.y The amplier valve 88 has the "is obtained from the output conductors 88 and control member thereof energized in accordance with the output voltage of the phase-shifting circuit 88. However, since valve .84 is nonconducting, no current is conducted by valve 88 and the transformer 21 is deenergized. The negative oidal voltage of intermittent character which appears during only those intervals that the load circuit is to be energized. As soon as the output voltage of the timer control appears, transformers 4l and l0: are energized. The output of transformer 4l appears as a positive bias across resistor 48 and renders the keying electric valve 34 conductive so that current is conducted through valve 34, resistor 38, and valve 35 to energize the transformer 21 with a sinusoidal voltage having a phase position dependent on the output voltage of the phase-shifting circuit Il. The transformer 2l may, to advantage, be a peaking transformer and thereby produce positive voltage impulses in the secondary windings 2i and 32 thereof sufllcient to render the firing electric valves 20 associated with electric valve means i3 and I8 conducting alternately at phase positions determined by the output of the phaseshifting circuit 53. As soon as current starts to flow to the load circuit through the valves i3 and I4, a voltage appears across the resistor 65 which has a magnitude dependent upon the magnitude of the current flowing and the adjustment of the taps on the resistors 11a. The conductivity of valve B and, as a result, the conductivity of valve means i3 and i4 is now controlled in accordance with variations in the voltage appearing across resistor 65, or in other words, in accordance with welding current. It has been found in practice that the current responsive voltage of resistor 65 and the intermittent reference voltage of resistor BB may be in the order of 400 volts and the preset or heat-control biasvoltage of the resistor 6l may be in the order of volts. As soon as the welding period is terminated by operation of the timer control, keying valve 34 becomes nonconductive and the voltages of resistors 65 and 66 disappear, returning the control of the valve 6B to the preset or heat-control bias of resistor il.

The relay 8| operates as a protective device to remove the regulator automatically if the current supplied to the load circuit exceeds a predetermined value. When the relay 8| picks up, contacts 8B and 86 are opened to deenergize resistors 65 and $6 and thereby return the control to the manual heat-control bias alone. The manual switches 19 and 92 provide means for/manually removing the current regulator from operation.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. An alternating current supply circuit, a load circuit, electric valve translating apparatus interconnecting said circuits and including electric valve means having a control electrode, a control circuit for energizing said control electrode to effect tfhe transmission of current to said load circuit, for a predetermined period or periods measured in cycles of said supply circuit and to render said valve means conductive at variable instants in the voltage wave of said supply circuit to regulate the magnitude of the current supplied to said load circuit, said control circuit comprising timing means for determining said period or periods, means responsive to said timing means for producing a reference voltage having ascenso a duration corresponding to the duration of said period or periods, means responsive to the current supplied to said load circuit for producing a regulating voltage, and means for energizing said control electrode in response to the algebraic sum of said reference voltage and said regulating voltage to regulate the magnitude of said load current.

2. An alternating current supply circuit, a load circuit, electric valve translating apparatus interoonnecting said circuits and including electric valve means having a control electrode, a control circuit forenergizing said control electrode to eect the transmission of current to said load circuit for a predetermined period or periods measured in cycles of said supply circuit and to render said valve means conductive at variable instants in the voltage wave of said supply to regulate the magnitude of the current supply to said load circuit, said control circuit comprising means for p ducing a timing voltage for determining said period or periods, means responsive to said timing voltage for producing a unidirectional reference voltage having a substantially constant magnitude during said period or periods, means responsive to the current supplied to said load circuit for producing a unidirectional regulating voltage of variable magnitude, and means for energizing said control electrodes in response to the difference in magnitude of said reference voltage and said regulating voltage to regulate said load current.

3. In combination, a supply circuit, a load circuit, electric translating apparatus interconnecting said circuits, timing means for controlling said translating apparatus to e'ect energization of said load circuit for a predetermined period or periods, a. regulating circuit including means for producing a voltage responsive to an electrical condition of said load circuit and having a duration -corresponding to the duration of said period or periods, means for producing a voltage which increases in magnitude abruptly at the beginning of each period of energization and decreases abruptly at the end of each period of energization, and means for controlling 'said translating apparatus during said period or periods in response to a. control quantity having continuously throughout said period or periods a value variable in response to variations in the algebraic sum of said voltages to maintain said condition substantially constant.

4. In combination, a supply circuit, a load circuit, electric translating apparatus interconnecting said circuits, timing means for controlling said translating apparatus t0 effect energization of said load circuit for a predetermined period or periods, a regulating circuit including means for producing a variable unidirectional voltage responsive to the current supplied t0 said load circuit, means controlled by said timing means for producing an intermittent unidirectional voltage recurring at intervals corresponding to each period of energization of said load circuit, and means for controlling said translating apparatus in response to the difference in magnitude of said unidirectional voltages to maintain said condition substantially constant.

5. An alternating current supply circuit, a load circuit, electric translating apparatus interconnecting said circuits including electric valve means having a control electrode, timing means for controlling the energization of said control electrode to determine the period or periods of energization of said load circuit and a phaseshifting circuit for regulating the current supplied to said load circuit comprising means for supplying an alternating current voltage, an output circuit and means including anelectric valve having a control member for controlling the phase of the voltage impressed on said output circuit with respect to said alternating-current voltage, means for producing a unidirectional voltage which varies in magnitude in accordance with an electrical condition of said load circuit, means `for producing a unidirectional voltage which increases abruptly at the beginning and decreases abruptly at the end o1' each period of energization oi said load circuit established by said timing means, means for producing an adjustable presety unidirectional voltage, means for energizing said -control member in accordance with the algebraic sum oi said voltages so that the phase relation of the voltage of said output circuit varies in accordance with said condition responsive circuit during periods of energization and is maintained at a preset phase position during periods of deenergization, and means responsive to said output circuit for energizing said control electrode.

6. An alternating current supply circuit, a load circuit, electric translating apparatus interconnecting said circuits including electric valve means having a control electrode, timing means for controlling the energization of said control electrode to determine the period or periods oi energization of said load circuit and a phaseshifting circuit for yregulating the current supplied to said load circuit comprising means for supplying an alternating current voltage, an output circuit and means including an electric valve having a control member for controlling the phase of the voltage impressed on said output circuit with respect to said alternating-current voltage means for producing a unidirectional voltage which varies in magnitude in accordance with an electrical condition of said load circuit, means for producing a unidirectional voltage which changes abruptly in magnitude at the beginning and end of each period of energization of said load circuit established by said timing means, means for energizing said control member in accordance with the difference o1' said unidirectional voltages so that the phase relation of the voltage of said output circuit varies in accordance with said condition responsive circuit during periods oi.' energization, means for establishing a predetermined yphase pomtion of the voltage of said output during periods of deenergization oi' said load circuit, and means responsive to said output circuit for energizing said control electrode. i i l 7. An alternating current supply circuit, a load circuit, electric translating apparatus interconnecting said circuits including electric valve means having a control electrode, an excitation circuit comprising a pair of electric valves in series for supplying voltage impulses to said control electrode when both said valves are conducting simultaneously, timing means forfcontrolling one of said electric valves to determine the cycles of said supply circuit during which the load is energized and a regulating circuit i'or controlling the other of said valves to determine the instant in said cycles `that said valve means is rendered conductive in accordance with an electrical condition of said load circuit comprising means for producing a voltage which varies in accordance4 with said condition, means controlled by said timing means for producing a reference voltage having one characteristic during periodsoi.' energization of said load circuit and a different characteristic during periods o! deenergization of said load circuit, and means for controlling said second electric valve in accordance with a combination 01' said voltages.

8. An alternating current supply circuit, a load circuit, electric translating apparatus interconnecting said circuits including electric valve means having a control electrode, an excitation circuit comprising a pair of electric valves in series for supplying voltage impulses to said control electrode when both said valves are conducting simultaneously to determine the cycles of said supply circuit and the instants in said cycles that said valve means is rendered conducting, timing means for controlling one of said electric valves and a regulating circuit for controlling the other of said valves in accordance with the current supplied to said load circuit comprising means for producing a unidirectional voltage which varies in accordance with said current, means controlled by said timing means for producing a unidirectional reference voltage having one characteristic during periods of energizationy of said load circuit and a different characteristic during periods of deenergization of said load cirf cuit, and means for controlling said second electric valve in response to the diil'erence of said voltages.

, BERTRAM G. HIGGINS. 

